Activity 2.6 NCERT Class 10 Science, Acids, Bases and Salts

Activity 2.6 NCERT Class 10 Science, Chapter 2 Acids, Bases, and Salts.


This activity asks us to add a few drops of phenolphthalein into dilute sodium hydroxide and see what happens when we add dilute acid.

Observation: A time comes after adding acid that pink solution of phenolphthalein disappears. Now again if we start adding sodium hydroxide it becomes pink.


Activity 2.6 NCERT Class 10 Science
Phenolphthalein in basic solution,.

Phenolphthalein is a colourless reagent. It turns the solution into pink at basic PH. So, It is used in an acid-base titration to see the endpoint. Like here adding acid neutralises the base present in the test tube. Now at the endpoint of the reaction, the addition of an extra drop of acid makes the solution acidic. As a result, the pink colour disappears.

Situation reverse when we add a base to this acidic solution. As a result, the solution gets own previous pink colour.

Inference/conclusion: A change in colour of PH indicator can indicate the completion of a reaction.

Next: Metal oxides react with acids to form its salt, Activity 2.7.

Read also: Metal carbonate reacts with acids to form carbon dioxide, Activity 2.5.

See the discussion on some other PH Indicators at Activity1.1.

Know more about phenolphthalein, Wikipedia.

5 thoughts on “Activity 2.6 NCERT Class 10 Science, Acids, Bases and Salts”

  1. Anshu Raj Sinha

    Very useful , before reading this it was hard to understand. But now after going through these pages ,it made me understood these activities very clear to me.
    Thank you studdy.

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